Desktop 3D printer

3D printers produce plastic parts under computer control. The process of 3D printing is especially useful for the smaller insect-class bots, where weight is a severe limitation to design. However, even Heavyweight-class builders use 3D printing to make composite reinforced components, custom compartment insulators, and wire guides. Keeping electrical parts and cables away from metal plates and sharp edges reduces the risk of damage and short circuits.

3D Printing is widely used in one specialized division of combat robotics, the Plastic Ants class, where the chassis and weapons (if any) must be made of plastic in order to qualify.

If you don't own a 3D printer, you may be able to get help from your local library or makerspace, or from your fellow bot-builders. Some people will want to design their own bots, which requires knowledge of 3D modeling using a computer or app for the purpose. Others will choose to download a premade design (see below). Once you've got a bot design working to your satisfaction, you can print a supply of replacement plastic parts, which can be used for repairs after your bot becomes damaged.

Selecting a Printer

Selecting a printer for 3D printing a combat robot can be a big decision, and here are some factors to think about when purchasing your printer.

Budget

Desktop and office 3D Printers can range from as low as $150 to over $10,000 depending on their hardware, capabilities, build volume, and other factors. Here's a quick overview of what's available:

Budget-friendly/hobbyist 3D printers: Range from $150 - $800, normally limited in materials and build volume. These include machines like the Creality Ender 3 series, and will normally have a maximum nozzle temperature of 245-250° Celsius. These machines are meant for printing PLA, PETG, and ABS, but with varying degrees of modification can print more advanced materials like Nylon and TPU.
Advanced materials printers: Range from $800 - $3,000, and are capable of printing materials like PLA, ABS, PETG, TPU, Nylon, Nylon Composites, and Polycarbonate blends with minimal or no aftermarket modification. Maximum nozzle temperature around 295° Celsius.
Engineering grade printers: Range from $3,000 - $10,000+, with few materials outside of their capabilities. These printers are often able to print not only advanced materials but also multiple materials using multiple extruders or multiple tool heads, allowing for even greater complexity. Dual extrusion can allow for a multi-color part (Black PLA/White PLA), multi-material finished product (PLA/PETG), or soluble support material like PVA/BCOH.

Printable Filaments and Materials

The materials that a FDM (Fused Deposition Modeling[1]) 3D printer can extrude must melt at a given temperature, maintain a consistent flow of material through the nozzle, and solidify in a consistent fashion. These materials include thermoplastics, waxes, and even chocolate! With specialized printers it is possible to use such materials as ceramics, glass, and concrete.

Most 3D prints in combat robotics will be made from rolls of plastics and plastic composites on an FDM printer. "Resin" printers are becoming more common in larger sizes at budget-friendly prices, and more options for resins are available to purchase on a regular basis.

The list of common 3D printable plastics below proceeds roughly from weakest to strongest.

PLA

PLA is inexpensive, but brittle.[2] It is the most common 3D printing filament. It rarely warps in use and is great for tiny parts.[3] It's a great starter material, and recommended for printing prototype parts. Many builders prefer other plastics, especially for their active weapons or armor. Pure PLA is made from cornstarch[4] and gives off a corn syrup odor which reminds some people of waffles.

PLA+

Various manufacturers offer "PLA+" and/or "Tough PLA," which are modified PLA filaments that are meant to be less brittle. With an acrylic additive, for instance, it may show much better impact resistance.[5] Inland and eSun claim their PLA+ products are 10x stronger than regular PLA.

PETG

PETG (a copolyester) is more heat resistant, more flexible, and less brittle than PLA.[6] It is well suited for 3D printing mechanical parts. Since it is more likely to flex under impact its resilience may be useful to the bot builder, but it is 2-3% heavier than PLA. Observe manufacturer's recommendations when printing, as it tends to stick very strongly to smooth print beds. You'll notice a fairly mild hot-plastic odor when printing.

ABS

ABS is a strong and reasonably impact-resistant material at a moderate price, but warps easily and smells worse while printing. Its low density makes it one of the lightest of all printable plastics (PLA is about 20% heavier for the exact same print). You'll probably need to print it in an enclosure for best results; this keeps its temperature even during printing, so that it only shrinks after printing instead of curling or warping during printing. Many hobbyists ventilate the enclosure to the outdoors with fan(s) due to the odor.

Nylon

Nylon is tough and flexible. Regular nylon is hygroscopic and must be kept in dry storage, or it will absorb moisture from the air and become spoiled after a few weeks. Consider buying a hybrid nylon material that doesn't require as much attention to storage.

PC

Polycarbonate is super strong - your robot arena walls are probably made from it! Many printers can't print it, though, because it must be heated to an extreme temperature (about 275°C or 525°F).

CF Materials

Carbon-fiber reinforced materials are extremely tough, and ideal for combat robotics. These are usually polycarbonate or nylon with chopped fibers embedded inside. You should strongly consider using these when plastic parts are needed for beetleweight designs.[7] This material requires a hardened printing nozzle, as the carbon-fiber strands or particles are highly abrasive.

Tips and Best Practices

Nearly all 3D printers can handle PLA and PLA+. Most other materials require printing onto a heated surface (the "print bed"). Check the specifications and instructions of your printer to find out what materials it can handle.
A basic limitation of 3D printed parts is that they can crack or break apart along layer lines, since they are made from layers of plastic. Generally, the tougher the plastic the more likely the layers will also hold together.
Pay attention to the orientation of parts on the print bed - consider orienting parts so that the direction that needs to be the strongest lies horizontal during printing.
You can make adjustments each time you print. Thicker walls (shells) and a higher percentage of infill add density and strength to your bot, but also increase weight. Remember to re-weigh your bot after changes have been made.

Robots you can Print

There are dozens of robot designs on Thingiverse and other sites which you can download and print; typically these will include several parts that are assembled to become the body and working parts of the robot. Some have helpful instructions and buying suggestions for finishing the working parts. Many have little or no guidance, and you may need some experience to try them.

Here is a partial list of bots on Thingiverse. Limited consideration has been given to whether each of these is buildable, or will meet the stated weight class.

3D Printing

Contents